High quality cutting blades are typically sharpened by using cylindrical abrasive wheels that are interlocked to form a nip. The blade passes axially along the abrasive wheels at the nip and material is removed forming facets on each side that intersect to form the sharpened edge of the blade. Standard practice utilizes successive stations of different coarseness to grind and finish the blade. Each station includes a pair of spindles and wheels and the associated mechanism to position and rotate the wheels. Thus, a first station utilizes coarse grit abrasive wheels to remove the largest amount of material. Subsequent stations utilize finer grits to hone the edge and frequently, a stropping station finishes the edge by straightening spot turn and removing burrs therefrom.
The interlocking of the wheels is typically accomplished by threading the pair of abrasive wheels with right and left hand grooves, respectively, and using a synchronized power transmission system to orient the groove of one wheel to the land of the other wheel. Alternatively, a plurality of spaced narrow abrasive discs can be used in place of the helically grooved wheels, with the discs of one assembly being interlocked with the discs of an oppositely positioned assembly.
The present invention relates to an improved method and apparatus for sharpening a blade in a single station and not finishing the edge at the end of a wheel.
Multi-station blade sharpening devices are known in the patented prior art as evidenced by the Bindszus U.S. Pat. No. 2,692,457 and the Delafontaine U.S. Pat. No. 2,709,874. Bindszus and Delafontaine represent six and five station processes as typical for the manufacture of quality blades. The five-station process includes two grind stations, a rough hone, a medium hone, a final hone and a stropping station. As those familiar in the art would know, the initial and ongoing adjustments of a process with five abrasive stations is quite complex.
The process described in the Nissen et al U.S. Pat. No. 3,461,616 reduces the number of stations required for blade manufacture. Nissen et al discloses three separate stations including a grinding station, a first honing station, and a final honing station, the wheels of the final honing station being tilted relative to the direction of travel of the blade. In traditional or straight honing stations, alternating lands of the wheels slightly deform the edge of the blade in an alternating fashion at the exit of the honing wheel assembly producing a condition referred to as spiral turn. With the process described in the Nissen patent, the edge is formed at the beginning of the final honing assembly and the edge is not in contact with the wheels at the exit. This eliminates the need for a stropping station. A drawback to the Nissen arrangement is that these fine grit hone wheels must theoretically remove material instantaneously at the entrance to the honing assembly.
When an abrasive wheel forms a facet on a blade, patterns of scratch marks or striations are left on the surface of the facet by individual grains of the wheel. In an untilted abrading station, these striations are arranged in a pattern of lines virtually perpendicular to the edge of the blade. With a tilted finishing station, the striations of the grind facet are still perpendicular, but those on the hone facet are inclined at an angle.
Further reduction in the number of stations required for sharpening a blade is described in the Atwater U.S. Pat. No. 4,807,401. Here a dual-station blade sharpening apparatus in which the grinding and honing stations are tilted in opposite directions relative to the direction of travel of the blade is disclosed. This station arrangement results in a blade with striations in the grind facet arranged at a first angle relative to the edge and striations in the hone facet arranged at an oppositely-positioned angle to the edge. While an improvement over the prior three-stage sharpening devices, the Atwater apparatus still suffers from the drawback of requiring removal of the bulk of honed material at the entrance to the honing station.
The present invention was developed in order to overcome these and other drawbacks of the prior devices by providing a single station blade sharpening method and apparatus.
Accordingly, it is a primary object of the invention to provide a blade sharpening method and apparatus wherein a single pair of opposed grinding assemblies are mounted for rotation about parallel axes and define a nip for receiving a blade. The apparatus is capable of generating a multi-faceted blade. The grinding assemblies each include a first portion at an entry end for progressively removing a first portion of the blade to significantly reduce the amount of material to be removed in subsequent portions. A second portion of the grinding assemblies is adjacent to the first portion and hones the cutting edge of the blade at the desired included angle. The grinding assemblies also include a third portion adjacent to the second portion and at an exit end of the assemblies for removing material back from the edge at included angles lower than the edge facet. A support structure positions the grinding assemblies at an angle with respect to the direction of travel of the blade. The striations formed on the first and second facets thus extend at the same angle relative to the blade edge.
According to another object of the invention, the first and third portions of the grinding assemblies have relatively coarse grits and the second portion of the grinding assembly has a finer grit.
It is a further object of the invention to provide opposed specially contoured abrading wheels for the grinding assemblies. The wheel diameter varies from the entry end to the exit end on a functional basis. The third portion of the wheels which forms the lower angled facets do not contact the first facets honed by the second fine grit portion of the wheels.
According to another object of the invention, the wheels contain grooves arranged in opposite directions so that the wheels interlock to define a nip.
According to an alternate object of the invention, the grinding assemblies each comprise a plurality of spaced coaxial discs with the discs of the opposed grinding assemblies interlocking to define a nip.